The heartbeat signal of the living body is important information of the living body. Conventionally, there has been used an electrocardiographic induction device that detects, as the heartbeat signal, an electrocardiogram obtained through a plurality of ECG electrodes attached to the living body. For example, devices disclosed in Patent Documents 1 and 2 are examples of such a device. The electrocardiogram is called as electrocardiographic induction waveform or ECG waveform, and R wave contained in the electrocardiogram is characterized to have a considerably clear pulse shape, so as to be easily detectable. Thus, the electrocardiogram obtains reliability as a substitution as the heartbeat signal in general monitoring of a patient at a medical site.